The invention relates to the field of RF toll collection wherein, in a roadway environment, vehicle borne transponders communicate with a stationary reader or readers to establish the toll for the vehicle carrying the transponder.
Patents relating to such field include:
U.S. Pat. No. 4,104,630 August 1978 Chasek
U.S. Pat. No. 4,303,904 Dec. 1, 1981 Chasek
U.S. Pat. No. 4,870,419 Sep. 26, 1989Baldwin et al
U.S. Pat. No. 4,937,581 Jun. 26, 1990 Baldwin et al
U.S. Pat. No. 5,132,687 Jul. 21, 1992 Baldwin et al
U.S. Pat. No. 5,164,732 Nov. 17, 1992 Brockelsby et al
U.S. Pat. No. 5,192,954 Mar. 9, 1993 Brockelsby et al
U.S. Pat. No. 5,196,846 Mar. 23, 1993 Brockelsby et al
U.S. Pat. No. 5,289,183 Feb. 22, 1994 Hassett et al
For conventions herein, the traffic flow eastbound and from left to right in the drawings may be thought of as representative of all directions.
Toll Plaza is the name for the toll collection point.
Electronic Toll Collection may be shortened to xe2x80x98ETCxe2x80x99.
By xe2x80x98transaction managerxe2x80x99 is meant a device for coordinating an upstream and a downstream reader, toll processing calculator, and locator.
xe2x80x98Point of Entryxe2x80x99 data or ETC data; includes sufficient information to calculate the toll charge and usually includes: point of entry, toll plaza ID, vehicle class and transponder ID.
A wide area is an area materially wider than the width required by a lane for a roadway vehicle hence a wide area roadway is materially wider than a single lane highway.
A wide area reader is typically used for a wide area RF communication system incidental to toll collection. The wide area capture zone is typically 16.8 meters (55 feet) wide by 36.6 meters (120 feet) long. The wide area reader typically uses a protocol known as Time Division Multiple Access (TDMA).
A lane based reader controls reader channels, each one of which corresponds to an individual vehicle lane which will communicate with a vehicle in an individual lane. A lane communication capture zone is typically 1.2 to 2.4 meters (4-8 feet) long and 3 meters (10 feet) wide. A vehicle in a lane capture zone may be uniquely identified.
Time Division Multiple Access (TDMA) is the preferred communications protocol in the upstream capture zone.
A conventional TDMA frame consists of a header known as a Frame Control Message (FCM), four data slots and sixteen activation slots of the type known as slotted Aloha. The FCM directs up to four transponders individually to transmit or receive in the four data slots. The activation slots are shared by all transponders on a random access basis to allow the transponder to notify the reader of its presence. A TDMA frame is approximately 10 ms long.
In this development it is preferred to extend the conventional TDMA protocol, to include optional new added fields desirable for communicating with a Smart Card toll system and at the same time maintain compatibility with the conventional TDMA system.
The preferred added fields may include:
Application Identifier Fieldxe2x80x94This field is used to inform the transponder which application is running in the reader, so that upon wake up, the transponder can initialize the on board device accordingly. Under the development, as described herein, the reader will only operate in accord with the first or wide area protocol. However, other applications, not part of the toll collection system described, may be added at another time.
Frame Number Fieldxe2x80x94This field is used by the transponder for antenna tracking and switching.
Antenna Number Fieldxe2x80x94This field is used by the transponder for antenna tracking.
Antenna Tracking and Switching Controlxe2x80x94This field is used by the transponder to select the antenna tracking and antenna switching so that it can be dynamically controlled by the reader.
Media Request Activation Control Field (MRA)xe2x80x94This field is used by the reader to command the transponder whether to transmit an MRA after the required process is completed.
Protocol Control Fieldxe2x80x94This field is used by the reader to command the transponder to go to sleep mode or to switch to lane based protocol after the first protocol is complete.
The added fields maybe arranged in any order in their position at the start of the FCM frame.
The TDMA system with the added fields is referred to herein as xe2x80x98extended TDMAxe2x80x99.
xe2x80x98Superframexe2x80x99; In the system preferred herein there are four TDMA (preferably extended) RF channels. A superframe is a complete cycle of the four channels by the TDMA Reader with one frame being cyclically transmitted on each antenna. A superframe for four channels is approximately 40 ms in duration.
xe2x80x98IDxe2x80x99; means xe2x80x98Identificationxe2x80x99.
xe2x80x98Tagxe2x80x99; is sometime used herein as a synonym for transponder.
xe2x80x98Upstreamxe2x80x99 and xe2x80x98Downstreamxe2x80x99; herein relate to position relative to traffic flow. Vehicles move from an upstream position to a downstream position.
A reader is a stationary transmitter receiver which enters into RF communications protocol with a vehicle borne transponder. The preferred embodiment uses a wide area reader which, upstream, enters into a first communication protocol with a vehicle borne transponder and a second or lane based reader which downstream, provides a plurality of channels each for an individual lane, one of which enters into a second protocol with the same transponder.
A principal variant of the invention uses, for RF communication, a transponder equipped with a Smart Card which may be electronically and mechanically coupled thereto, usually being optionally detachable. This variant as well as the description as a whole relates to the methods of using the Smart Card. The Smart Card equipped transponder is used in a roadway environment having a first reader defining an upstream RF communication or xe2x80x98capturexe2x80x99 zone designed to communicate with vehicle borne transponders over a roadway area wider than a single lane, to obtain from the transponder information for a transaction manager allowing the calculations as to toll amount and payment status. The data thus obtained is associated with the transponder ID and a second lane based downstream reader is connected to receive by downstream RF communication the status of payment and transponder ID.
The lane based readers are designed to define downstream communications zones designed to associate the transponder ID and payment status uniquely with vehicle travelling in an individual lane. Preferably the lane based reader is connected to a lane controller which directs the vehicle carrying the subject transponder to stop or go in accord with the payment status.
In a preferred variant of the invention the transponder provides the first reader with the information from the transponder and its Smart Card including the balance from which the toll may be deducted. This information is provided to calculating and coordinating means, here called a transaction manager, which calculates the toll and directs the Smart Card via the first reader and transponder to debit the toll amount and deduct it from the account balance. Then the Smart Card provides a completion message which includes: a payment status report, which may be xe2x80x98paidxe2x80x99; xe2x80x98insufficient balancexe2x80x99 or another condition; a certificate of payment to the transaction manager; and a signature for the financial institution. The transaction manager is equipped to report the payment status independent of the transponder and Smart Card to the second reader which is adapted to deal individually with the vehicles and which will physically associate the status and vehicle ID with a vehicle then in an individual lane and customarily direct the vehicle with the subject transponder usually by means of light signals typically attached to a lane controller.
The process as described provides the required security of financial information and account balances unlike the prior art use of a single reader. The use of a transaction manager provides a communication path from the wide area reader communication zones to the lane based reader which parallels that of the vehicle borne transponder. The transaction manager also provides a highly fraud proof method of securely confirming a successful operation. In a preferred mode of ensuring the security of the transaction, described in detail hereafter, the Smart Card, on the successful completion of a toll transaction, after debiting the account balance, calculates a two part message (called a certificate of payment).
The transaction manager independently calculates the two part message. One part of the Smart Card originating version of the certificate of payment is sent to the transaction manager for comparison. The second part of the Smart Card version of the certificate of payment is sent to the downstream reader for comparison with the second part of the transaction manager originating message. If the two comparisons coincide the debit transaction has been complete. This is discussed in more detail hereafter.
A transponder may be equipped with visual aids such as red, green, blue and/or yellow light emitting diodes (LEDs) which may be ON or OFF or intermittent. A transponder may be equipped with a buzzer which maybe ON or OFF or intermittent. Such light or sound means are customarily actuable by a reader, to sensibly signal the vehicle operator.
In a preferred aspect of the invention, an extended version of the TDMA protocol is used at the wide area reader. A TDMA reader can communicate with up to four different transponders per frame, by placing up to four different transponders IDs in the Frame Control Message transmitted at the beginning of every frame. Interference is avoided by having the transponder examine the Frame Control Message, and only if it observes an ID matching its own, can a transponder receive or transmit data.
A channel is the path for a signal, including signals between a transponder and a reader. In this application, the first or wide area reader, preferably supports four channels each of which may have a number of antennas each of which communicates with a number of transponders in time separation mode. In this application, second or lane based readers preferably support a channel for each lane at the toll plaza. There are typically 10-20 lanes and up to 8 channels (and antennas) per lane based reader.
In a preferred arrangement, a number of first reader fixed antennas may be provided and these are synchronized so that no meaningful interference may occur between fixed antenna radiation. If a channel is transmitted by more than one antenna, the channel system is provided by an RF splitter with antennas carrying the same channel space as far apart as possible to provide a geographical separation between antennas broadcasting on the same channel.
In a preferred variant of the invention, the channels of the second readers, each typically providing a channel for each lane up to seven lanes, are synchronized with each other and with the first readers.
In a preferred embodiment of the invention all fixed readers transmit at a different frequency than the transponders so that transponder transmissions which tend to be much weaker than those from fixed transmitters are not interfered with.
In a preferred variant of the invention a frame based transmission is used at the first reader so that this provides contention resolution between transponders communicating with the same antenna. Preferably the frame based system used is the Time Division Multiple Access (TDMA) system known as the xe2x80x98Slotted Alohaxe2x80x99 and described in U.S. Pat. Nos. 5,425,032 and 5,307,349, both to Shloss et al.
In a preferred variant of the invention, multiple (here four) channels of the first reader are provided preferably broadcasting in cyclical sequence the TDMA or extended TDMA frames (such sequence defines a superframe). Thus the upstream first reader antennas may be spaced from each other so that, in the event that a channel is being broadcast from two antennas simultaneously, the antennas are geographically separated to avoid interference at a transponder.
Where multiple upstream antennas are used, these are preferably sought intermittently by a transponder. The transponder is preferably time synchronized to receive a selected antenna for communication while sampling a number of antennas, say four, for comparative quality of service, i.e. transmission and reception. An algorithm preferably provides control of a switch for changing antennas and to call for switching at any time from one antenna to an antenna whose quality of service is consistently highest.
The algorithm for antenna selection and switching shown hereafter contains, as shown, several features. The number of superframes whose frame reception numbers are to be compared is chosen. A threshold number limits the comparison to antennas whose frame are received above a selected frame minimum in the N superframes. A number is subtracted from an antenna""s count for heavily loaded antennas. A hysteresis factor requires an unconnected candidate antenna to have a selected higher frame count than the connected antenna before being connected, to avoid too frequent switching.
In a preferred form of the invention a locator antenna system is provided. This may operate in accord with the system described in U.S. Pat. No. 6,025,799 issued to Ho et al., or U.S. Pat. No. 5,227,503 issued to O""Connor et al. Whatever the approach taken, the locator antenna system is used to determine, by triangulation and in terms of probability, whether the subject transponder (identified by its ID and coordinated by the transaction manager) is located inside the first (wide area or upstream) communications zone as opposed to being located outside the roadway associated with the subject capture zone or travelling the reverse direction.
In a preferred form of the invention, the locator provides probability thresholds; two of which are used for probability assessment. At a lower level (preferably 95% certain), it allows communication of the transponder information from the upstream reader to the transaction manager, and at a relatively higher certainty level (preferably 99.995%) it allows the debit transaction to be completed and acknowledged between the upstream reader and the transponder and Smart Card.